The present invention relates to an optical storage medium. Particularly, this invention relates to an optical storage medium having an information-visible zone indicating additional medium-related information.
Compact discs (CD) and digital versatile discs (DVD) are popular optical storage media.
Single-substrate-type optical storage media such as CDs have an information-visible zone on a label layer indicating additional medium-related information on the medium surface opposite to the signal-reproducing surface, by silk screen printing or offset printing.
In contrast, dual-substrate-type optical storage media such as DVDs do not have a space for such a label layer due to their disk diameter of 120 mm, center-hole diameter of 15 mm and inner storage-zone diameter of 46 mm, like CDs, thus, recording additional medium-related information being impossible.
In order to overcome such a problem, Japanese Unexamined-Patent Publication No. 10-143924 (1998) discloses “OPTICAL INFORMATION RECORDING MEDIUM”. The recording medium has two transparent disk substrates, formed on each substrate is a recording layer. The substrates are stuck to each other so that the recording layers face each other. Visibly printed on the disk surface, on which a laser beam is to be incident for reproduction, is a light-absorptive discoloring material, in accordance with the recorded contents.
Such printing is feasible for ROM- and dual-substrate-type DVDs because the recorded contents will not be changed.
On the contrary, RAM-type DVDs require rewritable information visibly formed thereon, related to the recorded contents, because users are allowed to rewrite the recorded contents.